The invention relates to a method of recognizing speech pauses in a speech signal which may have noise signals superposed on them.
Methods of this type are, for example, the prerequisite for the suppression of noise signals when telephone calls are made from an environment with acoustic disturbances. During the speech pause characteristic parameters of the noise signal are measured and employed to filter the noise before transmission substantially completely from the signal to be transmitted, using adaptive filters.
DE-AS No. 24 55 477 and corresponding to UK Patent Specification No. 1 515 937, column 10 discloses an arrangement in analog technique for recognizing speech pauses, which is based on the following method. The speech signal is divided into sections of equal lengths and a voltage value is obtained for each section by means of rectification and by taking the mean value, which voltage value is proportional to the average sound volume of the section. Finally, by taking the mean value during several speech sections a further voltage value is determined, which is proportional to the average loudness of the conversation. By comparing these two mean values it is determined whether a section is associated with a speech pause or not.
In the method of pause recognition no account is inter alia taken of the fact that, for example, unvoiced speech parts result in an almost total power reduction in the speech signal and that the relevant speech sections may therefore erroneously be recognized as speech pauses. Such faulty decisions occur in the prior art method more frequently according as the extent to which noise signals are superposed on the speech signal is greater.